This invention relates generally to magnetic head transducers and more particularly to a metal and ferrite composite magnetic video head transducer using sputtered strips for forming the core legs thereof.
The performance of a magnetic tape data recorder depends heavily on the properties of the magnetic materials used to make the recording heads and tapes and on the structural configuration of these materials which influence their magnetic properties. Magnetically hard materials, characterized by their high remanence, high coercivity, and low permeability, are chiefly used in the manufacturing of the recording tape and other related recording media. On the other hand, magnetically soft materials, which exhibit low coercivity, low remanence, and relatively high permeability, are commonly utilized to make the magnetic cores for the heads which are the means by which electrical signals are recorded on and reproduced from the magnetic tape.
The typical ring-type magnetic head is composed of two highly permeable magnetic cores, with a non-magnetic gap spacer and a coil to which signal information is connected. The record head is a transducer that changes the electrical energy from the signal system into a magnetic field that is emitted from a physical gap in the head which impresses a magnetic pattern on the magnetic tape proportional to the electrical signal. The reproduce head, conversely, is a transducer that collects the flux from the magnetic tape across a physical gap and changes it into an electrical signal that is proportional to the recorded flux.
Ferrite materials have been conventionally used as the magnetic material in video heads. The advent of high-definition video tape recorders, digital video tape recorders, computer digital data storage devices and the like, with the resultant use of high coercivity recording media such as metal powder media, metal evaporated media etc., have accelerated the trend towards high density construction for recording even larger amounts of information. As part of this evolution, there is the resultant need to increase the density of the information signal recorded on the medium. Conventional ferrite cores have significant limitations in providing the desired characteristics to achieve the required performance for these applications.
There are performance problems with ferrite heads, particularly when such heads are used with high coercivity magnetic tape, and particularly during the recording process. During recording, larger signals are required with high coercivity magnetic tapes than with conventional magnetic tapes. The problem is not severe with the use of a ferrite head during reproduce operations, since signal levels from the tape are much lower in magnitude. With higher recording signals, the signal tends to drive the ferrite heads into saturation. During reproducing or "playback", it has also been observed that there is a significant noise level resulting from contact of such high coercivity magnetic tapes with the ferrite heads, called multiplicative noise which, in turn, requires higher head efficiencies to achieve an acceptable signal-to-noise ratio. Bulk metal heads likewise have performance disadvantages, principally in that they have poor high frequency response.
The above considerations have led to the use in recording heads of any number of other commercially available magnetic materials which have higher flux density saturation, such materials including cobalt-zirconium-niobium (CZN) alloys, iron-aluminum-silicon alloys including Alfesil, Sendust, Spinalloy, or Vacodur each having a nominal composition of 85% iron, 6% aluminum, and 9% silicon, and also amorphous metals.
Besides the magnetic properties of the head core materials used, the critical design considerations that dictate performance of the heads are track width, gap length, gap depth, and core geometry (e.g. path length). Each of these parameters must be selected in accordance with the design criteria of the magnetic tape recorder, while, at the same time, maintaining the head efficiency as high as possible.
In miniaturized transducers, signal coupling is extremely important, and much of the efficiency is determined by the gap to core reluctance, that is, E=Rg/Rg+Rc. If the reluctance of the core is negligible relative to the reluctance of the gap, the efficiency approaches unity. In many instances, in miniaturized transducers, matching transformers are required for impedance matching and amplification to the preamplifier circuitry. However, such matching transformers introduce an additional element of noise in the signal. If a winding window in the transducer is simply made larger to accommodate more windings, the larger window area increases the magnetic path length and, in turn, reduces the head efficiency. To counteract this reduction in efficiency, a gap depth reduction can be made; however, this, in turn, reduces the life of the head or transducer.
Attempts have been made to provide transducers with better wear characteristics and longer life, for example, by plasma arc sputtering of an Alfesil layer on the tape contacting surface of a ferrite core transducer, such as shown and described in U.S. Pat. No. 3,566,045, issued to Paine on Feb. 23, 1971.
In U.S. Pat. No. 2,711,945, issued to Kornei on Jun. 28, 1955, a core of magnetically soft material is provided with metallic high permeability pole shoes which are disposed for contact with the moving tape, the poles being intended to provide a sharp well-defined, narrow transducing gap and thus avoid the attendant wear disadvantages of the soft core material which, in one embodiment is a ferrite or iron powder.
Composite video head transducers, such as the Kornei transducer have been around since the mid-fifties. Other such composite transducers utilized slabs or blanks of one material adhered to ferrite core material in side-by-side relationship. For example, one such transducer included a toroidally shaped ferrite core with first and second confronting Alfenol metal pole tips with a gap spacer between them and held in contact with a lateral surface of a slotted ferrite ring core, with the pole tips extending beyond the circumference of the ferrite ring core in a plane adjacent to the lateral surface. Another such composite head includes first and second generally planar Alfesil core blocks brazed together with a ferrite core member of shorter length abutted to one side of the brazed combination with the Alfesil core blocks protruding beyond the length of the ferrite core member. In both of these transducers the protruding portion contacted the tape during use.
There exists, therefore, a significant need for an improved high frequency magnetic transducer having an optimum number of signal windings with a short magnetic path to reduce core reluctance and to make the head efficiencies less dependent on the permeability of the magnetic material used in the magnetic cores, and to eliminate the need for a transformer. In addition, losses should be minimized, leakage reluctance should be reduced, and the core material must not be driven into saturation when used at normal recording signal levels. The fabrication of such a transducer should be high volume, high accuracy, low cost and achieve a high degree of uniformity. The present invention fulfills these needs and provides further related advantages.